As a means for coping with electronic components having a smaller size in recent years, a semiconductor device has been used that uses a stacked multi structure in which switching elements are layered to constitute a bridge circuit. A semiconductor device using a stacked multi structure is known from the following Patent Publication 1 for example. According to the semiconductor device disclosed in Patent Publication 1, an H-type bridge circuit using a power semiconductor element can be formed with an improved integration degree while decreasing an area occupied by a supporting plate. However, when a MOS-type field effect transistor (MOSFET) is used for layering power semiconductor elements, the chip size is increased to prevent a smaller size from being achieved. Thus, an insulated gate-type bipolar transistor (IGBT) that can realize a smaller chip size has been used. However, the use of the IGBT additionally requires an external diode to be mounted in an H-type bridge circuit. This has consequently prevented a smaller size from being achieved and has caused an increased product cost due to the external diode.
Generally, MOSFET includes, as shown in FIG. 5 for example, a semiconductor substrate (50) including an N-type conductivity type drain region (51), a P-type conductivity type base region (52) formed on an upper face (51a) of a drain region (51), and an N-type conductivity type source region (53) formed on an upper face (52a) of a base region (52); a gate electrode (55) formed on an upper face (53a) of the source region (53) via a gate insulating film (54); a source electrode (56) formed on the base region (52) and an upper face (52a, 53a) of the source region (53); and a drain electrode (57) formed on a lower face (51b) of the drain region (51). Thus, the P-type conductivity type base region (52) and the N-type conductivity type drain region (51) have therebetween a diode (58) that can be used as an inner diode to be protected.
On the other hand, the IGBT has, as shown in FIG. 6, a semiconductor substrate (60) that has a P-type conductivity type collector region (61), a first base region (62) of N-type conductivity type that is formed on an upper face (61a) of the collector region (61), and a second base region (63) of P-type conductivity type that is formed on an upper face (62a) of the first base region (62), and an emitter region (64) of N-type conductivity type that is formed on an upper face (63a) of the second base region (63); a gate electrode (66) formed on an upper face (63a) of the second base region (63) via a gate insulating film (65); an emitter electrode (67) formed on an upper face (63a, 64a) of the second base region (63) and the emitter region (64); and a collector electrode (68) formed on a lower face (61b) of the collector region (61). Thus, the IGBT is structured as shown in FIG. 6 so that a diode (69) is each formed between the second base region (63) of P-type conductivity type and the first base region (62) of N-type conductivity type and between the collector region (61) of P-type conductivity type and the first base region (62) of N-type conductivity type, respectively. Thus, the diodes (69) having reverse polarities are series-connected. This has caused a difficulty where this diode cannot be used as an inner diode for protection of transistor. In an H-bridge circuit in which an output terminal is connected with a load having an induction component for example, a back electromotive force caused by the induction component of the load tends to be applied to the IGBT. Thus, each IGBT must be connected in parallel to the diode to bypass current in a reverse direction (surge current) caused by the electromotive force via the diode.
The following Patent Publication 2 discloses an IGBT in which the center of a collector region has a cathode region having an opposite conductivity type and the upper part of the cathode region has a P-type conductivity type anode region to store a diode. According to the IGBT of Patent Publication 2, an external diode can be omitted and a semiconductor device having a stacked multi structure having layered IGBT can be formed.                Patent Publication 1: International Publication Number WO 2005/018001        Patent Publication 2: Japanese Laid-Open Publication No. H9-191110        